Methods and apparatuses using urea permselective diffusion through charged membranes

A urea separation apparatus comprising:

• a housing;
• a blood compartment located within the housing, the blood compartment being a part of an extracorporeal circuit fluidly connected to a patient and configured to receive blood of the patient via a blood pump;
• a waste membrane enclosing the blood compartment, the waste membrane configured to filter waste from the blood;
• a dialysis fluid compartment located on an opposite side of the waste membrane from the blood compartment, the dialysis fluid compartment being a part of a dialysis fluid circuit and configured to receive dialysis fluid from a dialysis fluid pump for absorbing the waste from the waste membrane;
• a charged membrane enclosing the dialysis fluid compartment, the charged membrane configured to filter at least a portion of the waste from the dialysis fluid;
• and
• a urea compartment located on an opposite side of the charged membrane from the dialysis fluid compartment, the urea compartment being a part of a urea circuit that circulates secondary fluid for absorbing the portion of the waste from the charged membrane.